1. Field of the Invention
The present invention generally relates to a copper bonding wire of a semiconductor package, and more particularly to a wire bonding structure of a semiconductor package, wherein a copper bonding wire includes a non-spherical block portion, whereby the bonding area between a pad and the copper bonding wire can be sufficiently maintained or increased.
2. Description of the Related Art
Referring to FIG. 1, according to a process for manufacturing a semiconductor package, the technology of wire bonding process widely applied to the electrical connection between a pad 11 of a chip 10 and a pad 13 of a substrate 12 by using a bonding wire 14. Wire bonding process is mainly based on gold (Au) wires, but copper (Cu) wire has an advantage of low cost. Compared with the gold, the copper has better electric conductivity and thermal conductivity, whereby the copper bonding wire has thinner diameter of wire and better dissipation of heat. However, the copper has disadvantage of insufficient ductility and easy oxidation such that the utilization of the copper bonding wire is restricted.
Recently, the copper bonding wire is only applied to a chip pad with a big size or low dielectric material (low-k) of wafer, because the success of the wire bonding process of the copper bonding wire depends on the structural strength of the chip pad. In order to avoid the failure of the wire bonding process of the copper bonding wire, the small size of the chip pad will be limited.
Referring to FIGS. 2 to 4, they depict a conventional method for bonding a copper bonding wire. Referring to FIG. 2, a copper bonding wire 20 is provided by a wire bonding machine, wherein the copper bonding wire 20 has a copper line 22 and a copper ball 24. The copper ball 24 is physically connected to an end of the copper line 22 by a discharging electricity manner or a burning hydrogen manner. Referring to FIG. 3, the copper ball 24 is pressed and then deformed. Referring to FIG. 4, the deformed copper ball 24 is bonded to an aluminum (Al) pad 32 by a vibration process. However, the hardness of the copper is higher than that of the aluminum, and thus the force resulted from the copper bonding wire 20 possibly damages the structure of the aluminum pad 32 during the pressing process. Furthermore, referring to FIG. 5, the boding interface 80 between the aluminum pad 32 and the copper bonding wire 20 in the prior art is a circular cross-section. If the exposed surface of the aluminum pad 32 is rectangular, the area of the circular cross-section cannot be nearly equal to the area of the exposed surface of the aluminum pad 32, i.e. the bonding area between the aluminum pad 32 and the copper bonding wire 20 cannot be sufficiently maintained. Accordingly, there exists a need for a copper bonding wire capable of solving the above-mentioned problems.